1. Field of the invention
The present invention relates to a method for processing a crosslinkable elastomeric composition comprising silica.
More in particular the present invention relates to a method for processing a crosslinkable elastomeric composition comprising silica by using at least one processing apparatus having an internal metal surface, said method comprising a pretreatment of said internal metal surface with at least one sulfur-free organosilane compound.
Moreover, the present invention also relates to a method for treating a metal surface with at least one sulfur-free organosilane compound.
Furthermore, the present invention also relates to a metal article having at least one surface which is at least partially coated with at least one coating layer comprising at least one sulfur-free organosilane compound.
2. Description of the Related Art
The treatment of metal surfaces with silane compounds, usually in order to prevent their corrosion, is known in the art.
For example, U.S. Pat. No. 5,750,197 relates to a method of treating a metal substrate comprising the steps of: (a) providing a metal substrate; (b) applying a coating of a first treatment solution directly onto the surface of said metal, said first treatment solution consisting essentially of at least one multi-functional silane having at least two tri-substituted silyl groups wherein the substituents are individually selected from the group consisting of alkoxy and acetoxy, wherein said multi-functional silane has been at least partially hydrolized, preferably fully hydrolized. Specific examples of multi-functional silanes which may be used are: 1,2-bis-(triethoxysilyl)ethane, 1,2-bis-(trimethoxysilyl)ethane, 1,6-bis-(trialkoxy-silyl)hexane [including 1,6-bis-(tri-methoxysilyl)-hexane], 1,2-bis-(triethoxysilyl)ethylene, 1,4-bis-(trimethoxysilylethyl)benzene, and 1,2-bis-(trimethoxy-silylpropyl)amine. An optional second treatment solution containing an organofunctional silane may also be employed, in particular if the metal substrate has to be painted. Specific examples of organofunctional silanes which may be used to carry out said second treatment, are: γ-aminopropyltriethoxysilane, γ-mercaptopropyl-trimethoxysilane, γ-ureidopropyltrialkoxysilane, γ-glycidoxypropyl-trimethoxysilane, and any of a variety of vinyl silanes (i.e., an organofunctional silane wherein the organofunctional moiety is a vinyl group) including vinyltrimethoxysilane, vinyltriethoxysilane, vinyl-triacetoxysilane. The abovementioned method of treating is said to give metal surfaces having an improved corrosion resistance.
U.S. Pat. No. 6,919,469 relates to a method for treating a metal substrate, comprising: (a) providing a metal substrate; and (b) applying a coating of a silane composition onto the metal substrate, the silane composition comprising at least one substantially unhydrolized aminosilane which has one or more secondary or tertiary amino group. Specific examples of amino-silanes which may be used are: bis-(trimethoxy-silylpropyl)amine, bis-(triethoxysilylpropyl)amine, bis-(triethoxysilylpropyl)ethylene diamine, N-[2-(vinyl-benzylamino)ethyl]-3-aminopropyltrimethoxysilane, amino-ethylaminopropyltrimethoxysilane. The metal substrates treated as disclosed above, are said to have an improved corrosion resistance and/or an improved polymer adhesion.
In the rubber industry, in particular that of tires manufacturing, it is known practice to use the so-called “white” reinforcing fillers, in particular silica, in total or partial replacement for the carbon black in order to achieve good mechanical properties (both static and dynamic), as well as low hysteresis.
It is also known that, in order to obtain a good degree of dispersion of the silica in the elastomeric compositions, it is necessary to subject the elastomeric compositions to a prolonged thermomechanical blending action. Moreover, in order to increase the affinity of the silica with the elastomeric polymer, it is necessary to use suitable coupling agents, such as, for example, sulfur-containing organosilane compounds. However, the use of said sulfur-containing organosilane compounds may cause some drawbacks during the processing of the elastomeric compositions to which they are added.
In particular, the Applicant has noticed that, during the processing of crosslinkable elastomeric compositions in processing apparatuses having an internal metal surface, e.g. a Banbury mixer, said sulfur-containing organosilane compounds may interact with the internal metal surface of said processing apparatuses (in particular, it may chemically react with the hydroxy groups present onto said metal surface) and may subsequently promote the adhesion of the elastomeric polymer onto the same. Consequently, the internal metal surface which becomes sticky and rough, has to be cleaned, usually manually, at the end of every processing cycle so causing a lengthening in the processing of the elastomeric compositions and a premature wear of the processing apparatus.